This invention relates generally to fluid control devices and, more particularly, to an electrically-modulated pressure regulator valve with a variable force solenoid.
As is known, solenoid-operated fluid control devices are used in a wide range of electrically controlled systems for controlling the pressure and/or flow rate of fluid discharged from a valve assembly in response to an electrical input signal supplied to a solenoid assembly. In many applications, a valve sub-assembly and a solenoid sub-assembly are integrated into a unitized fluid control device, commonly referred to as a solenoid valve assembly.
In a typical solenoid valve assembly, the solenoid sub-assembly has an armature which acts on, or is coupled to, a valve member in the valve sub-assembly. As is known, movement of the armature is responsive to the magnetic flux generated as a result of the electrical current applied to the electromagnetic windings of the solenoid sub-assembly. Thus, translational movement of the armature causes corresponding translational movement of the valve member for controlling the magnitude of the output pressure of fluid discharged from the valve sub-assembly. More particularly, fluid at an inlet pressure is delivered to an inlet port of the valve sub-assembly such that the position of the valve member regulates an output pressure generated at an output port of the valve sub-assembly as a function of the energized state of the solenoid assembly. Depending upon the particular design of the solenoid assembly, a change in energization level may cause a proportional increase or decrease in the output pressure. Such a proportional device is commonly referred to as a "variable force" solenoid valve assembly or "VFS". One example of a conventional variable force solenoid valve assembly is disclosed in commonly owned U.S. Pat. No. 4,947,893 wherein the axially movable armature of the solenoid sub-assembly is coupled to a spool valve that is supported for axial sliding movement within the valve sub-assembly. As is also disclosed in the above-referenced patent, it is common to provide a biasing spring to urge the spool valve in a predetermined direction.
In a typical solenoid valve assembly, an electrical conductor is wound around a bobbin through which is positioned in the radial center an armature displaceable relative to the bobbin in accordance with an electrical signal applied to the electrical conductor. Components having magnetically conductive properties may be arranged in proximity to the coil and armature assembly to provide a flux path therebetween. In one exemplary variable force solenoid configuration, an armature is retained for translational movement within a central bore of a bobbin on which an electrical coil is wound such that the armature is moveable in a first direction in accordance with an electrical signal applied to the coil and is normally biased in the opposite direction in accordance with the preload exerted thereon by a coil spring. The coil spring is disposed within a common longitudinal bore formed in the armature and bobbin with one end seated against the armature and the other end seated against a spring adjustment screw. The position of the spring adjustment screw can be selectively varied for calibrating the amount of preload exerted on the armature.
The presence of a biasing spring in a central bore of the armature presents some important design considerations. First, because the biasing spring must exert a sufficient biasing force to cause translational movement of the armature, which generally affects corresponding movement of the valve mechanism against mechanical fluid pressure, the armature typically requires an enlarged diameter in order to accommodate a sufficiently forceful biasing spring. Unfortunately, increasing the diameter of the armature consequently requires inducing a greater magnetic field therethrough to effect the same force as in a more compact armature/solenoid design. In turn, such an increase in the magnetic field requires a commensurate increase in either the number of coil windings or the electrical energy applied to the coil, or both. Generally, solenoid designers increase the number of turns of the coil winding, resulting in a solenoid assembly of even greater size, primarily to accommodate the armature-biasing spring. Thus, it is particularly desirable to provide a spring-biasing arrangement which alleviates this resultant increase in armature size and the related solenoid assembly components.
Furthermore, in order to calibrate variable force solenoid assemblies, secondary air gaps require adjustment via threaded magnetic elements in order to regulate the primary and secondary flux paths traversing the magnetic solenoid circuit and to provide a desired output pressure in response to a predetermined applied voltage. In typical variable force solenoid assemblies, it is also necessary to calibrate the biasing force of the spring as well, which is effected through adjustment of a spring adjustment screw. Such a design requires an iterative calibration process in which the spring-biasing force is first adjusted, followed by adjustment of the air gap to vary the flux path, followed by recalibration of the spring biasing force which is often displaced while calibrating the working air gap. While variable force solenoid assemblies described herein are accurately and sufficiently calibratable, the calibration process described herein requires additional manufacturing processes. Thus, it is further desirable to provide a variable force solenoid valve assembly in which the working air gap adjustment and the spring-biasing means are independently adjustable to provide more accurate and faster calibration.